1. Field of the Invention
This invention relates to a boria-promoted hydroprocessing catalyst which can be used for hydroprocessing heavy feeds.
2. Description of the Previously Published Art
Catalysts have been made for various processes where boron has been added.
U.S. Pat. No. 4,139,492 discloses a method of preparing hydrotreating catalysts with an impregnation solution of Group VIB compounds, Group VIII compounds and HBF.sub.4. U.S. Pat. No. 3,666,685 discloses a method of preparing hydrotreating catalysts with 1 to 5% boron phosphate. In these patents, the use of boria to control macropore volume was not recognized. Additionally, the high acidity which reagents such as HBF.sub.4 and boron phosphate impart to the supports make these catalysts less suitable for processing heavy feeds. The present invention does not require the use of HBF.sub.4 or boron phosphate.
U.S. Pat. Nos. 3,954,670 and 3,993,557 disclose a method of preparing hydrocracking catalysts by hydrolyzing a mixture of aluminum alkoxide and boron alkoxide. U.S. Pat. No. 2,713,037 discloses a method of preparing alumina containing catalysts by hydrolyzing aluminum alkoxide with water in the presence of a silica hydrosol, ammonium molybdate or boric acid. These methods of preparation differ from that of the present invention, which does not require the use of aluminum alkoxide. Aluminum alkoxide is relatively more expensive than conventional sources of alumina, such as those described in U.S. Pat. No. 4,154,812.
Boria-alumina supports have been used to make hydrocracking catalysts, such as described in U.S. Pat. No. 4,500,645, Japanese patent Nos. 57207546, 57141492 and 58020232 and French patent No. 2487220. However, these catalysts all contain an additional zeolitic component which is not required in the catalyst of the present invention. None of these patents discuss the promotional effect of boria in desulfurization.
A lube oil hydrocracking catalyst is disclosed in U.S. Pat. No. 3,617,532 which contains 8 to 15% boria. An aluminum borate catalyst made by mulling alumina with boric acid followed by extrusion is disclosed in U.S. Pat. No. 3,856,705. The specified level of boria was between 8 and 40%. The level of boria in these patents is higher than the range specified in the present invention and has been found to be detrimental to catalyst performance.
U.S. Pat. No. 3,018,244 discloses an isomerization and reforming process using catalysts prepared by impregnating Pt/Al.sub.2 O.sub.3 and Rh/Al.sub.2 O.sub.3 with H.sub.3 BO.sub.3 and HBF.sub.4. Boria was said to promote the isomerization activity. The promotional effect of boria in desulfurization was not mentioned, nor was the use of this type of catalyst in hydrotreating.
U.S. Pat. No. 4,399,057 discloses a method of preparing a catalyst support which has an average pore diameter of at least 180 Angstrom units, at least 0.8 cc/g of its pores between 0 and 1200 Angstrom units and at least 0.1 cc/g of its pores between 1200 and 50,000 Angstrom units. This catalyst support is prepared by heating a composite of two or more oxides, including boria and alumina, at a temperature between 1300.degree. and 1700.degree. F. in an atmosphere of steam. The present invention does not place such a restriction on the pore size distribution. Furthermore, we have found that heating the catalyst support up to such a high temperature will cause a lowering of desulfurization activity.